Gillibrand’s amendment would remove military commanders from the process of prosecuting sexual misconduct cases. Instead, independent military lawyers would determine whether to bring charges of misconduct. Her proposal is an effort to protect victims from retaliation by the chain of command.

McCaskill told reporters that inserting independent military prosecutors into the decision-making process wasn’t wise because they might refuse to take on difficult cases to protect their own “won-loss record.”

“If the prosecutors have the only say, we will have fewer prosecutions,” McCaskill said.

She cited past failed investigations of military sexual misconduct by civilian authorities as examples of the risk of removing the chain of command. Both civilian and military prosecutors currently have jurisdiction over cases that occur off-post.

“In just the past two years, we’ve had dozens and dozens of cases in which civilian prosecutors declined to prosecute, but commanders stepped forward and made the decision to proceed,” she added.

McCaskill was joined at a news conference by six female former service members, Sen. Kelly Ayotte, R-N.H., and Sen. Jon Tester, D-Mont., who agreed that the current pending Senate bill — co-authored by McCaskill — protects victims by ensuring that commanders will be held accountable for the actions of those under their supervision.

Gillibrand released information Thursday explaining her bill was drafted in direct response to testimony of victims and military leaders.

Gillibrand’s statement rejected the criticism, including the idea that independent military prosecutors would want to protect their win-loss record.

“This reflects a fundamental misunderstanding of how the military justice system works,” Gillibrand stated. “JAGs move back and forth between defense and prosecution assignments, so they are less concerned about their prosecution numbers … in the military, prosecutors are professionally graded on a whole host of matters — not just wins/losses. In fact, military prosecutors often receive praise from their superiors for being willing to take tough cases to trial.”

The pending bill was approved by the Senate Armed Services Committee in the wake of an investigative journalism project by the San Antonio Express-News that disclosed the frequent dismissal from military service of those who report sexual assaults. Many of those dismissals were based on bogus psychological evaluations.

Defense Secretary Chuck Hagel and top military commanders have objected to the Gillibrand proposal on the basis that it removes accountability in the chain of command and rejects the culture of military institutions.

McCaskill was the target of a recent ad campaign by Protect Our Defenders, an advocacy group for sexual assault victims that supports Gillibrand’s bill. The ad, which ran in Tuesday’s St. Louis Post-Dispatch, accused the Missouri Democrat of blocking effective zero-tolerance reform of sexual assault laws, a criticism that McCaskill, a former prosecutor of sex crimes, said she found shocking.

The advocacy group also created an online petition titled “Where’s Claire?” urging her to support Gillibrand’s legislation. The petition had almost 1,000 signatures as of Thursday evening.

Sen. Carl Levin, D-Mich., chairman of the Armed Services Committee, continued his criticism of the Gillibrand amendment by releasing two letters defending the existing military chain of command.

A letter from Adm. James Winnefeld, the chief of Naval Operations, claimed that civilian law enforcement often fails to pursue cases that military commanders subsequently push to prosecute. The other letter, penned by Army Gen. General Richard Gross, reported that the United Kingdom, Canada, Australia, New Zealand, the Netherlands and Germany did not see any improvement in reporting by victims of sexual assault when those nations reformed their military justice systems to remove the chain of command.

“This data is more evidence that shifting this authority from commanders is likely to mean fewer courts martial and reduced odds that victims will get the justice they deserve,” Levin said.

In response, Gillibrand’s office stated: “It is not surprising the military leadership is shifting the goal posts and fighting hard to protect the status quo. … To suggest that commanders do not have a role under the Gillibrand proposal is wholly inaccurate. Secondly, the military has failed to note any statistical or anecdotal evidence that good order and discipline has eroded due to our allies’ independent military justice systems.'”

Gillibrand’s amendment failed in the Armed Services Committee by a 17-9 margin, but has since picked up the support of 41 legislators, including Sens. Ted Cruz of Texas, Rand Paul, R-Ky., Mark Kirk, R-Ill., and Michael Bennet, D-Colo. Gillibrand needs 51 votes to pass the amendment.

Kirk, a former intelligence officer in the Navy Reserve, said Gillibrand’s proposal was “common sense” in the face of an “unacceptable status quo” amid military brass.

“This proposal will strengthen commanding officers’ zero-tolerance command climate when it comes to sexual assault and enable our service members to stay focused on the task at hand,” Kirk said.

A Pentagon report released in May estimates 90 percent of the 26,000 service members who were sexually assaulted last year did not report the offense while 60 percent of victims who reported the offense said they experienced retaliation.